Separation of mixtures of liquid and solid fatty acid compounds



United States Patent 3,549,676 SEPARATION OF MIXTURES OF LIQUID AND SOLID FATTY ACID COMPOUNDS Helmut Hartmann, Langenfeld Rhineland, and Werner Stein, Unterbach, Germany, assignors to Henke] & Cie G.m.b.H., Dusseldorf, Germany No Drawing. Filed Aug. 3, 1967, Ser. No. 658,023 Int. Cl. Cllb 15/00 US. Cl. 260-419 Claims ABSTRACT OF THE DISCLOSURE A process is disclosed for the separation of liquid and fatty acid compound mixtures into components of different melting points by forming a dispersion of the fatty acid material having a temperature higher than the separation temperature in an aqueous solution of a surface active material having a temperature at which separation into liquid and solid components takes place and thereafter separating the dispersion in the conventional manner. According to the invention, it has been found that particularly favorable results are obtained if this process is carried out by cooling the fatty acid mixture in a first stage to the extent that only a portion of the fatty acid that is to be separated in solid form crystallizes out and thereafter, in a second stage, the resultant fluid-crystal mass is further cooled by dispersing the same in an aqueous solution of a surface active material having a temperature lower than that of the fluid-crystal mass, i.e., to a temperature at which separation takes place.

This invention relates to improvements in the separation of mixtures of liquid and solid fatty acid compounds. It more particularly relates to the separation of these mixtures into components of different melting points.

Processes for the separation of liquid and solid fatty acid compound mixtures have been described, which consist in forming a dispersion of the fatty acid material in an aqueous wetting agent solution at a temperature at which the mixture contains solid and liquid components, and thereafter separating this dispersion into its components by any of the known methods. The separation can be carired out, for example, by filtration; the components of the dispersion being separated according to states of aggregation, liquid fatty substance and aqueous wetting agent solution being produced as the liquid component of the dispersion and solid fatty substance being produced as the solid component of the dispersion. The separation can also be carried out independently of the state of aggregation of the phases present in the dispersion by using fully jacketed (i.e., imperforate) centrifuges, the phases being thereby separated into layers of different specific gravity. When the dispersion is subjected to centrifugal action in an imperforate centrifuge, the aqueous phase containing the solid fatty acid particles pass over as the specifically heavier fraction and the liquid fatty acid particles separate as a specifically lighter fraction. This lastdescri-bed separating process has acquired particular practical importance as a continuous industrial process.

The fatty acid substances to be processed according to this invention include fatty acid esters of both natural or synthetic origin and particularly natural fatty acid esters, most particularly the triglycerides, as well as fatty acids and fatty alcohols. A procedure of particular importance to date for separating fatty acid esters and fatty acids has been described in US. Pat. 2,800,493, while US. Pat. No. 2,972,636 describes a process for separating mixtures of fatty alcohols.

Of special economic importance is the separation of mixtures of liquid and solid fatty acids, and particularly those having 8 to 30 carbon atoms in the molecule, and

more particularly those having 10 to 20 carbon atoms in the molecule. A particularly important industrial mixture is that of olein and stearin. The invention shall hereinafter be described with reference to the separation of mixtures of fatty acids. The invention, however, is not limited to such mixtures, but is applicable to all similar mixtures, regardless of their source or procedure for obtaining the same, and is equally applicable to the separation of mixtures of fatty acid esters, and especially mixtures of triglycerides and fatty alcohols, as would be obvious to the skilled artisan, since the separation is physical in nature.

In the prior-art processes, the fatty acids which are to be separated are usually first completely melted and thereafter chilled to the separating temperature. For the cooling of the fatty acid mixtures. Scraper coolers (Votator) are generally employed. These involve cylindrical cooling devices through which the fatty acid mixture flows and in which the cooling surfaces which come into contact with the fatty acid material are kept free of deposits of solid fatty acids by means of moving or rotating scrapers. A crystalline mass is thus formed, and the further the starting material is cooled, the stiffer the resultant crystalline mass. Consequently, the separation as above described suffers from the drawbacks that to carry out the process, relatively sturdily constructed scraper coolers are required in order to handle fatty acid mixtures which are very stiff at the seperating temperature, and also because the heat transfer between -the coolant and the fatty acid mixture becomes poorer as the pasty consistency of the latter increases; either the throughput becomes low or disproportionately large cooling surfaces are required. This diminishing heat transfer cannot be improved by lowering the temperature of the coolant at will, because then not only will the higher-melting fatty acids be separated out at the excessively cooled walls of the cooler, but also large amounts of lower-melting fatty acids which are supposed to remain in the liquid fraction.

In accordance with the invention it has now been found that the above-described diificulties in the process of separating mixtures of fatty acid materials can be avoided by carrying out the crystallization in two stages; i.e., if the starting fatty acid material is cooled in a first stage in the conventional manner to the extent that only a portion of the fatty acid that is to be separated in solid form crystallizes out, and if, in the second stage, the further reduction of the temperature of the fluid crystal mass formed in the first stage is brought about by forming a dispersion of this fluid crystal mass in an aqueous solution containing a wetting agent and having a temperature lower than that of the fluid crystal mass.

It has proven advantageous to carry out the separation by first chilling the fatty acid mixture in a standard cooling apparatus, such as the above-mentioned scraper cooler, to such an extent that about 30 to and preferably 40 to 70%, of the total solid fatty acid to be removed is crystallized out. When this condition has been achieved, the fluid to slurry-like liquid fatty acid containing solid fatty acid particles in a second stage is admixed with a chilled aqueous solution of wetting agent. The quantity and temperature of the aqueous solution of wetting agent is advantageously adjusted so that, after the temperature exchange has taken place between the fatty acid mixture and the wetting agent solution, the desired separating temperature is reached. As the aqueous solutions of wetting agent often contain electrolytes such as organic salts or other organic substances, such as an organic water-soluble solvent which reduces the freezing point of water, such as glycerine, polyvalent alcohols or other water-soluble ethers, as, for example, ethylene glycol, glycerine, propylene glycol, polyglycolene, polyglycerine, etc., the temperature of 3 the wetting agent solution can easily be reduced even below the freezing point of water. If necessary, crushed ice can also be stirred into the fatty acid mixture together with the aqueous wetting agent solution.

The vessel in which the precooled fatty acid and cold wetting agent solution are mixed together should be insulated against thermal exchange with the usually warmer surroundings. The insulation can be replaced by a cooling jacket; the temperature of the coolant in the cooling jacket being maintained at the same temperature as the desired final temperature of the fatty acid or slightly below same.

It is not necessary to adjust the desired final temperature in this stage of the process: the dispersed fatty acid mixture can be cooled together with the aqueous wetting agent solution down to the separating temperature, or if the dispersion has cooled below the separating temperature, it can be warmed back up to it.

The quantity of the aqueous solution of the wetting agent employed generally amounts to 75 to 300%, preferably 100 to 200%, of the weight of the fatty acid mixture being separated. The temperature of the wetting agent solution depends on the temperature of the fatty acid added, the desired final temperature, and the ratio of the amounts of fatty acid mixture to wetting agent solution employed.

The process according to the invention can be combined with the process according to German Patent 970,292. In the latter process, a wetting agent solution is used for the dispersal of the mixture of fatty acid crystals and liquid fatty acid in which the concentration of wetting agent is greater than it is to be in the final dispersion, and then the dispersion is brought to the final concentration by the addition of water or a more dilute wetting agent solution. In this process, too, the dispersion of the fatty acid mixture in the Wetting agent solution can be cooled down to the separating temperature if the latter has not yet been reached by mixing with the chilled wetting agent solution.

The process according to the invention facilitates the cooling of the fatty acid mixture, and simplifies it by eliminating a portion of the otherwise necessary scraper cooling equipment, and it increases the throughput of existing installations. It is true that the wetting agent solution has to be chilled before it is combined with the fatty acid mixture; nevertheless, this does not produce any separation of crystals, so that scraper coolers are not required for the cooling of the wetting agent solution. Furthermore, the transfer of heat from the fatty acid mixture through the wetting agent solution to the cooling brine is better than in the case of the direct cooling of the fatty acid mixture by the cooling brine. As a result, the process of the invention makes possible for the first time a highly eflicient and economical separation, being excellently suited for commercial operation with high throughput efficiency and low cost.

The following examples are illustrative, but not limitative of the present invention.

EXAMPLE 1 In this example, the process of the invention is compared with a comparable prior-art process, both processes being carried out on a laboratory scale. A cylindrical vessel, 20 cm. in diameter and 30 cm. high, provided with a stirrer, was used for the cooling of the fatty acid and of the dispersion of the fatty acid in wetting agent solution. The stirrer was U-shaped and was centrally mounted in the bottom and in the cover of the vessel. The vertical stirring arms which were dimensioned so as to pass close to the cylinder wall were provided with strips of plastic which, when the stirrer was in motion, scraped along the vessel wall. In carrying out the described experiments, the vessel was immersed in ice water.

In four parallel experiments, 2000 g. of distilled tallow fatty acid (acid number 206; saponification number 207; iodine number 52.3; hardening point 40.5 C.) were in each case cooled to such an extent that the higher-melting fatty acid fraction or a portion thereof separated by crystallization. Thereafter, within 10 minutes, 4000 g, of aqueous wetting agent solution were introduced with stirring. The solution contained 2% MgSO and 0.2% sodium decyl sulfate by weight. The temperature of the Wetting agent solution was maintained at between and 5 C., depending on the temperatures of the fatty acid mixtures with which they were combined. In Experiment 1c, the stated quantity of wetting agent solution contained of its weight, i.e., 400 g., of finely crushed ice, the stated concentrations of magnesium sulfate and sodium decyl sulfate being based on the condition after the melting of the ice.

In Comparative Experiment 1a, the fatty acid mixture was chilled to the final temperature in the scraper cooler without the addition of wetting agent solution, and then mixed with the wetting agent solution which had been brought to the final temperature.

In Experiment 1b, the temperature of the dispersion to be separated was lowered by the addition of chilled wetting agent solution, not to the final temperature of 5 C., but only down to 19 C. Thereafter, the fatty acid mixture and wetting agent solution were further chilled together by external cooling.

Further details of the condition of the experiments and of their results will be seen in the table following the examples. The table also contains information on the quantity of fatty acid that separated in the preliminary cooling, in percent of the total amount of higher-melting fatty acid to be separated, the amount of time required for the individual stages of the process, the characteristics of the products obtained, and the throughput increase that can be achieved according to the invention. The process of the invention provides for an increase in throughput to more than twice that which is possible in the known process.

EXAMPLE 2 The starting material employed in this example was distilled cottonseed oil fatty acid (acid No. 204; saponification No. 206; iodine No. 96; hardening point 34 C.). The fatty acid was supplied at a temperature of 35 C. and was used in two parallel experiments, the one (Example 2a) comprising the prior-art process, and the other (Example 2b), the process of the invention. In contrast to the process described in Example 1, a somewhat smaller quantity (3000 g.) of wetting agent solution was used, the

same being added somewhat more rapidly, so that the time required for stirring in the wetting agent solution amounted to 5 minutes.

The results of these experiments can be seen in the table. It will be observed that the process of the invention makes it possible to put through, i.e., process, twice the amount of fatty acid without appreciably altering the characteristics of the end products.

EXAMPLE 3 In this example, the procedures described were carried out in an industrial apparatus. The continuous cooling of the fatty acid mixture was conducted in 5 scraper coolers arranged in series and having a total cooling area of 20 square meters. The first two scraper coolers were cooled with water having a temperature of 20 to C., and the last three were cooled with brine having a temperature of from 10 C. to 2 C. From the scraper coolers, the thickflowing fatty acid mixture was introduced into the first chamber of a trough which was divided by perforated partitions into five chambers arranged in tandem. In these chambers, the wetting agent solution or the wetting agent solution diluent was added to the fatty acid mixture. The material emerging from the last chamber in the trough was separated in a full-jacket centrifuge into liquid fatty acid as the lighter layer, and dispersion of solid fatty acid in wetting agent solution as the heavier layer.

In a first experiment which corresponds to the procedure of the prior art, a distilled tallow fatty acid (acid No. 206; saponification No. 208; iodine No. 51.1; hardening point 41.0 C.) was chilled from 45 C. to 5 C. The maximum fatty acid throughput that was possible under these conditions amounted to 1050 kg./hr.; i.e., if the throughput was increased, the fatty acid was no longer chilled to the required end temperature of 5 C. The emerging fatty acid was thoroughly mixed in the first chamber of the trough with 5 kg./hr. of a 50% solution of sodium decyl sulfate and 400 l./hr. of a 2% MgSO; solution, both at 5 C. Another 400 l./hr. of 2% MgSO solution at 5 C. was fed to each of the following chambers. Accordingly, approximately 2000 1/hr. of wetting agent solution at 5 C. was consumed in the dispersing of the 1050 kg./hr. of fatty acid mixture. The liquid fraction produced in the centrifuge had a turbidity point of 4 C., while the iodine number of the solid fraction amounted to 16.3.

In the second experiment, the procedure just described was modified according to the invention. The throughput of fatty acid was increased to 2000 kg./ hr. Since the coolant throughput and the temperature of the coolant remained unaltered, the fatty acid emerging from the final scraper cooler had a temperature of 19 C., at which the fatty acid flowed into the first chamber of the trough. There, 10 kg./hr. of 50% sodium decyl sulfate solution and 800 l./hr. of 2% MgSo solution at C. were added. The remaining chambers were each supplied with 800 l./hr. of 2% MgSO solution at 0 C., so that the 2000 kg./hr. of fatty acid mixture was dispersed into approximately 4000 L/hr. of Wetting agent solution. The dispersion left the trough, which was refrigerated externally with brine at -2 C., at a temperature of 5 C. After separation in the full-jacket centrifuge and removal of the solid fatty acid from the wetting agent solution, an olein having a turbidity point of 4 C. and a stearin having an iodine number of 16.8 were recovered. Thus, the fatty acid "fractions obtained had substantially the same characteristics as those obtained by the prior-art process; the throughput, however, had been approximately doubled in the same apparatus.

components of the mixture and a specifically heavier phase of aqueous medium with substantially solid com ponents of the mixture suspended therein, the improvement which comprises, in a first :stage, cooling the said fatty acid mixture from a higher temperature to a temperature at which only a portion of the fatty acid that is to be separated in solid form has crystallized out; thereafter, in a second stage, cooling the resultant fluidcrystalline mixture by dispersing the same in said aqueous solution of a wetting agent having a temperature lower than that of said fluid-crystalline mixture.

2. Improvement according to claim 1 wherein said cooling in said first stage is effected so that to 85% of the material to be separated from the starting material in solid form has crystallized out.

3. Improvement according to claim 1 wherein said cooling in said first stage is effected so that to 70% of the material to be separated from the starting material in solid form has crystallized out.

4. Improvement according to claim 1 wherein said cooling in said second stage is effected using said aqueous solution of wetting agent in an amount of 75 to 300% of the weight of the fatty acid mixture being separated.

5. Improvement according to claim 1 wherein said cooling in said second stage is effected using said aqueous solution of wetting agent in an amount of 100 to 200% of the weight of the fatty acid mixture being separated.

6. Improvement according to claim 1 wherein said aqueous solution of wetting agent employed in said dispersing has a concentration of wetting agent higher than that required in the final dispersion to be separated, the concentration of wetting agent in said dispersion being lowered following the formation of the dispersion.

7. Improvement according to claim 6 wherein said concentration of wetting agent is lowered by addition of water thereto.

8. Improvement according to claim 6 wherein said concentration of wetting agent is lowered by addition of a dilute aqueous solution of wetting agent.

9. In the method for the separation of mixtures of fatty acid compound into components of different melting points by forming a dispersion of such a mixture in an aqueous OPERATING CONDITIONS AND RESULTS OF EXPERIMENTS ACCORDING TO EXAMPLES 1 AND 2 Characteristics of the Comparison between state of Cooling in scraper cooler Production of dispersion fatty acid fractions art and invention Possible Time required by throughprocess up to put with Amount of Wetting completion of the same fatty acid agent Solid Fatty dispersion separating Cooling crystallized solution Dispersion Time fatty acid efiect, time in in percent temperatemperarequired acid, Liquid, turb. in in percent Exp. minutes of Exp. a ture, C. ture, C. in min. I No. I 0. point minutes of Exp. a a=100 51 100 5 5 10 21. l 88 4-5 01 100 I00 7 O 1 l9+5 l 10+15 22. 5 88 4-5 32 52 191 16 72 2 0 5 10 22. 0 89 4-5 26 43 235 22 81 0 5 10 20. 8 89 4-5 32 52 191 41 100 5 5 5 32. 4 128 45 4 5 100 100 16 58 2 0 5 5 33. 1 128 4-5 211 46 220 1 In Example 1b, after the mixing together of the fatty acid and wettin lished itself, which was then lowered by external cooling 2 10% as ice.

g agent solution (time required: 10 min.) a temperature of 19C.estab- (time required: 16 min.) t0-,l:5 0.

solution of sodium decyl sulfate as a wetting agent at a temperature at which the mixture contains both solid and liquid constituents and thereafter separating the aqueous dispersion into a specifically lighter phase of substantially liquid components of the mixture and a specifically heavier phase of aqueous medium with substantially solid components of the mixture suspended therein, the improvement which comprises, in a first stage, cooling the said fatty acid mixture from a higher temperature to a temperature at which only a portion of the fatty acid that is to be separated in solid form has crystallized out; thereafter, in a second stage, cooling the resultant fluid-crystalline mixture by dispersing the same in said aqueous solu- 5 tion having a temperature lower than that of said fluidcrystalline mixture.

10. Improvement according to claim 9 wherein said fatty acid mixture to be separated is a mixture of stearin and olein.

References Cited UNITED STATES PATENTS 3,052,700 9/ 1962 Waldmann et al 260419 3,458,545 7/1969 Faur et al 2604l9 FOREIGN PATENTS 970,292 9/1958 Germany 260419 LEWIS GOTTS, Primary Examiner 10 E. G. LOVE, Assistant Examiner 

